Conventional pulleys are made of various materials, including polymeric materials and metals such as iron or steel, many of which are affixed to the shaft by various means such as a key or key way to cause the pulley and shaft to rotate together. To avoid having to remove the shaft and bearings when it was necessary to replace a pulley, it has long been known to utilize a split pulley. Such a pulley is shown, for example, in British Patent No. 4685 issued Mar. 5, 1901 to John Lumsden. To decrease manufacturing costs, prior art pulleys have been made of plastics as disclosed in U.S. Pat. No. 4,506,559, issued Mar. 26, 1985 to Francke, et al. The prior art teaches a variety of means to hold split pulleys together. For example, U.S. Pat. No. 438,822 patented Oct. 21, 1890 by G. Philion discloses the use of a pair of hoops to hold his split wooden pulley together and G.F. Dable, in his U.S. Pat. No. 3,159,047 issued December 1, 1964 uses a pair of split flexible spring steel rings. Wiegand, et al, in their U.S. Pat. No. 4,631,974 use two or more circular band clamps around the hubs of a sprocket, together with a pair of wedge dog clamps, to hold a split sprocket together.
Despite the availability of a large variety of pulley constructions, there are still many applications for which no suitable pulley configuration has been found. For example, in many mining operations, such as coal mining, mined material is transported on a conveyor belt which may be hundreds of feet long. The return side of the conveyor belt tends to droop and sag, so it is necessary to provide means to support it. It has been the practice to support such belts on a series of pulleys mounted on shafts which extend transversely of the conveyor belt. These shafts are mounted on pillow block bearings, so that the pulleys and shaft are rotated by the moving belt resting on the pulleys. Since such belts may be from four to twelve feet wide, there may be five to fifteen pulleys mounted on a single shaft, and shafts may be spaced as closely as ten feet apart for a distance of hundreds of feet.
The environment surrounding such conveyors is often laden with abrasive particles, and to retard the effect of such particles on the pulleys, they are often made of an abrasion resistant material such as rubber, which may be reinforced by an embedded steel ring. The pulleys are installed on the shaft by driving them on one end until they are spaced as desired along the shaft. Such pulleys have a bore which is an interference fit on the shaft, and include axially extending slots spaced around the bore, which allow the bore to be spread to facilitate installation. The shaft is then installed in the bearings.
Despite the use of abrasion resistant materials, these pulleys wear fairly rapidly, and must be replaced. Since they are normally mounted fifty feet or more above the ground, replacement is a major, labor-intensive operation. As a result, the usual replacement operation consists of assembling pulleys and bearings on the shafts on the ground, using a crane to lift the assembly to the installation location, removing and discarding the old assembly, and then installing the new assembly.